Sorry dumb question but I'm barely starting to understand tunes and stuff, what happens if you stick to pumping 91 and you get stage 2? Do you just lose hp? Thanks guys

Its possible that if you go stage 2 with more boost, the engine will start to detonate or pre ignite from using a low octane fuel such as 91 and it will retard the ignition timing to reduce the combustion knock. This will make the car perform slower and could possibly hurt then engine.